In a photovoltaic power generation system which performs power generation using solar light, generally, a plurality of photovoltaic modules are connected in series to constitute a photovoltaic string, and a plurality of photovoltaic strings are connected in parallel to constitute a photovoltaic array. An output from this photovoltaic array is supplied to a load device such as a power conditioner and is supplied to a commercial power system or the like.
In such a photovoltaic power generation system, when there is insulation failure in the photovoltaic array, for example, when a person or an object touches an insulation failure point or when the insulation failure point and a metal stand or the like come in contact, a ground fault at which an electrical circuit comes in contact with the outside in an unintentional form may occur. Conventionally, for example, a ground fault detection device described in Patent Literature 1 is known as a device which detects this ground fault. In the ground fault detection device disclosed in Patent Literature 1, a value of a current flowing from an electrical path of a grounded photovoltaic array to the ground is measured, and the ground fault of the photovoltaic array is detected when this current value exceeds a current setting value, which has been set in advance.